Thermal process for producing pure tantalum and columbium compounds



Patented June 12, 1951 EFICE THERMAL PROCESS FOR PRODUCING PURECOMPOUNDS TANTALUM AND 'CGLUIWBIUM Daniel Gardner, New York, N. Y.

No Drawing. Application September 14,1946,

Serial No. 697,152

10 Claims.

This invention is a n vel thermal process for producing pure tantalumand columbium and certain compounds thereof, being adapted for theconversion or reduction of certain starting materials containing theseelements to yield the pure metals, or either of them, suitable forvarious industrial purposes. In referring to columbium it is to beunderstood that this is the same element also Well-known in certaincountries under the alternative name of niobium.

Much of the data, and certain of the condi-- tions, relating to thesetwo elements or metals,

referred to. The symbol R may be used to desig-- hate either or both ofthe metals Ta and Cb. In

this application all recited temperatures are to be understoodas thoseof the Centigrade system. The present invention is characterized inbeing directed to the production of Ta and Cb through their sulphides,and the complete process may for convenience be considered in two stepsor stages, combinable to merge one into the other; and such respectivesteps may preliminarily be considered in a general Way as follows. Thestarting material may contain or consist of one or more of the followingmore important industrial compounds of Ta and/or Cb, namely, thepentoxide, the pentachloride and the pentafluoride; and the processhereof, thermal in character, may deal with the compound or compoundseither of Ta or of Cb, or of both of these, especially when found in thesame raw material or mineral. The first step then consists in thethermo-chemical treatment of the starting compound, or compound-mixture,to convert the Ta and/or Cb content thereof to the sulphide or sulphidesof such element or elements. Next, in the second step or reaction, andpreferably after the sulphide of Ta and/or Cb has been freed ofseparation may be suitably efiected at the outset or at the sulphidestage of the process.

It is believed that the present invention is novel inthe outlinedprocess in its entirety, and as well in the sub-process involving thedescribed first step or reaction, yielding the sulphide of the metal ormetals, and also in the sub-process outlined in the second step as apractical means of reducing the sulphide to the desired metal or metals.

The general objects of the present invention are to afford theeconomical production of the metals Ta and/or Cb, by a process and stepswhich are practical and reliable, to yield the pure metal or metals. Anassociated object is to afford the practical conversion of thepreviously mentioned starting compounds of Ta and/or Cb to the sulphidesthereof, and the isolation of said sulphides in pure form, irrespectiveof the described further steps or reactions thereon; and a furtherobject is to afford a practical way of reducing the pure sulphide orsulphides to the metals. Other objects and advantages of thepresentinvention will appear in the reading of the hereinafter followingdisclosure of oneor more embodiments thereof, or will be understood bythose conversant with the subject. Y i

In this application the treatments of the materials and compounds ofboth Ta and Cb'are intimately combined and described, for the reason,among others, that said elements are in some respects closely analogousand related, both of them being in periodic group V, each of them havingits more usual valence of five, both having veryhigh melting and boilingpoints, and both of them being found in common in certain naturalcompounds or minerals; and it is part of the present discovery that theintermixed compounds of the two may be treated in unison for theirconversion and reduction.

'Since the general subject in discussion is relatively novel and recent,that is, having had but little intensive research and development, it isdeemed appropriate to precede the description of the invention by ageneral outline of certain pertinent portions of the past history andavailable present data concerning the two elements tantalum andcolumbium.

Through the extensive research of Biltz & Kirchner (Berichte, vol. 43,p. 1645, 1910) the formulae of the sulphides of tantalum and ofcolumhium (niobium) have finally been established as being TaSz andCbSz. However, numerous published assertions, starting with Rose (Pogg.Annalen, vol. 99, of 1856 and again vol. 105, of 1858) have been made,often of a very contradictory nature, believed to be due chiefly to thefact that the authors, who, although they A similar reaction, accordingto Rose, can be obtained by using carbon disulphide vapor or gas at atemperature around 960 C.; if a higher temperature is used, as somewherebetween 1200 and 1300 the sulphide obtained is crystalline. Thus, forTa:

Similarly, when dealing with columbium, at temperatures respectivelysomewhat lower, the above equations become:

Cb+2S=CbS2+147.0 Cal.

Cb+CSz=CbSz+C+1690 Cal.

The following table gives the principal data concerning the two metalsand their sulphides,

namely, their molecular weights (M. W.) densities (D); melting points(M. P.); boiling points (B. P.) heats of formation (ht. f.); specificheats (sp. ht); and solubilities (sol.); using also such conventionalabbreviations as d. for decomposes, sl. for slightly, exc. for excess,and ra. for ratio of B. P. to M. P.

Table of properties Property alkali The above figures for the sulphideswere estabished to applicants satisfaction on the basis of sulphides ofhighest purity. As already stated, prior workers, notwithstanding impureingredients, found some valuable reactions, which help to explain thenature of the two sulphides. The following previously tried reactionsmay be cited:

Biltz & Kirchner, cited supra, proposed to obtain tantalum sulphide byacting on tantalum pentoxide with vapors of carbon disulphide, thereaction starting at 650, but this requiring a high increase intemperature to improve the yields, and being never really satisfactory.Their reaction was as follows:

Ta205+3H2S+CS2= 2'I'aSz-I-3I-I2O+CO2S+126.5 Cal.

On the other hand Rose (supra) suggested passing HZS vapors to reactwith Ta pentachloride TaCl5; B. P. 242, at red heat; or heating tantalumpentoxide, in a current of hydrogen charged with vapors of carbondisulphide, as follows:

Similarly, for columbium, these reactions would become:

Applicant has carefully considered these reactions and has found them togive poor yields, even when working with purest ingredients, which thequoted authors never have had at their disposal. One of the proofs ofthe impurity of the sulphides formerly produced is that the earlierauthors disagreed even as to the color of the compounds, not to mentionthe more important items, such as density, structure, melting point,etc.

Still less satisfactory results have been obtained for producingcolumbium sulphide, where the authors cited the obtaining of anoxysulphide only, especially since the results thereof that were longago published by Delafontaine (Arch. Sci. Phys. Nat. (2), vol. 27, p.167, 1866).

Under the recited circumstances and absence of successful outcome, asindicated, applicant turned his attention to other ways of producing Taand Cb sulphides and metals, guided by the following considerations: (a)tantalum and columbium sulphides are definitely stable compounds; (2))these two sulphides must be obtained free from all possible impuritiesfor successful final results; (0) these sulphides can be obtained inmutual mixture as well as when separated, since, as will be seen below,the best reactions for their production are rigorously similar, althoughthe temperature data of the two sulphides are somewhat difierent; (d)both sulphides, when mixed, can be jointly reduced from the sulphideform to the mixed metals, or can be first fully separated from eachother as sulphides (or even earlier) and reduced separately to themetals; (e) the two sulphides, once obtained in their purest form, areso stable, that they are attacked only by a mixture of hydrofluoric andconcentrated fuming nitric acids,

a condition which in itself is absolutely technically non-existent innature and is a strictly artificial development; (I) the two puresulphides, recoverable in mixture or separately, may be treated as inthe nature of intermediate or subproducts irrespective of theutilization to which they are put. 7

Applicant has heretofore conducted research with special reference toindustrial applications of the more common hydrides, particularly whenthe reactions involved are of the exothermic type. Also, using carbondisulphide CS2 as a source of sulphur, as in his prior applications andpatents relating to the production of light metals (magnesium,beryllium, etc.), applicant has particularly studied the reaction whichoccurs between carbon disulphide and a hydride, such as a saline hydrideor alkaline earth hydride, for example calcium hydride CaHz; and hasdetermined the following among other equations:

From his subsequent researches upon the compounds of Ta and/or Cbapplicant has discovered that related equations are usefully availablefor desirable treatments of these compounds, such as the pentoxides oftantalum or columbium, or to equal or greater advantage thepentachlorides thereof (and the pentafluorides but to less advantage canalso be treated). As examples the following equations are recited,useful for the conversion of Ta and/or Cb pentoxide or pentathis Thesereactions have the following advantages, especially when using thepentachlorides (less notably for the pentafiuorides) in accordance withthe invention: (1) each of these reactions proceeds quantitatively; (2)all byproducts become volatilized, or can be otherwise easily removed;(3) the recovered products, Ta and/or Cb sulphides, are of supremepurity; temperatures of these reactions are moderate or low, notdepassing or exceeding red heat (about 650 to 750) when the pentoxidesare treated, and considerably lower when the pentachlorides(orpentafluorides) are treated; and this fact of operation at lowertemperatures in part accounts for the extreme purity of the sulphidesobtained.

In all cases the reaction atmosphere must be considered; and it shouldbe of an inert gas, such as A or He or Ne, or at least a non-oxidizinggas such as hydrogen or a hydrocarbon, to pr clude interference with thedesired reaction.

By way of review ofthe above described first step or reaction, theprocedure thereof may be stated asza thermal process, which ispreferably continuous by being performed with travel through thechambers of the furnace. Said step operates .to sulphidize or convert astarting compound of Ta and/or. Cb to the sulphide or sulphides thereof,said compound, in a practical aspect,- consisting of the availablepentoxide and/or pentachloride and/or in some cases the pentafluoride.This step or reaction of producing the sulphidesconsists, withoutrepeating the hereinabove set forth equations used, in mixing thestarting compound in powdery condition (that is, pulverulent, granular,flaky etc.) with the following agents; (a) a sulphur agent, for which 5fumes may be used, but preferably carbon disulphide, CS2, a liquid whichunder rise of temperature quickly vaporizes, and (b) a nonsulphurhydride or equivalent agent, such as a saline or an alkaline earthhydride, preferably calcium hydride Cal-I2, or, Bali-I2 or Lil-I; (orsometimes the silicides or borides may be used) also in powdery form,and then heating such mixture to a moderate temperature, of the order ofseveral hundred degrees, e. g., in the neighborhood of 600 to 700;thereby causing the aforesaid reaction wherein the starting compound isconverted to the sulphide TaSz and/or CbSz. These recovered sulphidesare adapted readily to be brought to pure condition by elimination ofthe reaction byproducts and any impurities, as by gasification, or inthe case of CaO by dissolving it in HCl.

As a following or second step or reaction the thermal treatmentsdescribed may be continued for the sequential reduction of the sulphideto the metal Ta and/or Cb. By this second step the pure sulphide, stillin powdery form, and which may be still hot from the previous step, isreduced to the metal by first mixing with such sulphide a suitablereducing agent as the pyro- (4) the genetic metal aluminium, also inpow'dry form;

or sometimes but less preferable can be used Mg or Be or Li. Suchaluminium should be in molecular proportion, or preferably in a somewhatgreater proportion, to convert surely the entire S content to aluminiumsulphide A1283 in accordance with the equation hereinbelow recited. Suchmixture is next brought'to a moderate temperature of about 659 or withina range, not critical, of about 150 thereabove or therebelow, therebybringing about an exothermic reaction, with the formation of the A1283;and thereafter the temperature is progressively ele-. vated to 1550, orrather slightly thereabove, thereby. causing the A1283 to distil orsublime away, leaving behind the recovered pure metal Ta and/or Cb,which may still be in powdery form. The pyrogenetic character of the-'Al helps to elevate the temperature andkeep it high.

Supplementally,'if both of the R metals (Ta and Cb) are present in suchproduct they may be separated from each other, for example, in one ofthe ways desecribed in said copending ap plication, or by the known wayof converting the mixture into an oxyfluotantalate mixed with anoxyfluocolumbate, these possessing such differences in solubility as tofacilitate their separa tion; followed by reconversion to the respectivemetals. 1

Reverting to the reduction of the sulphide or sulphides to metal, by useof Al powder, according to'Goldschmidts reaction, the equations may6TaSz+8Al=4Al2S3+6Ta+3832 Cal.

6CbS2+8Al=4 Al2S3+6Cb+4=972 Cal.

The reduction step so characterized possesses the process value that theA12S3, which is readily attacked by moisture, has the very high heat offormation of 344.8 CaL, and melts at 1100and distills off at 1550; whichlatter is not merely below the boiling points of Ta and Cb butalso iswell below themelting pointsthereof, 2850 and 1950". As a consequence agood temperature margin exists, ensuring the complete separation away ofthe A1283, which in itself is a byproduct of value and can even be usedagain to regenerate the S vapors or compounds needed. for the first stepof the process described. Due to the high melting points of. the reducedTa and/or Cb these elements can be maintained in powdery form during thereduction, this fact materially enhancing the effectiveness andcompleteness of the reduction, and yielding a final product in a mostconvenient condition.

The described process, considered either in its entirety or in itsrespective steps, may be carried on in batch manner, as in one or asuccession of crucibles; or it may be preferred with travel throughfurnace chambers as a continuous process, between infeed and discharge,with better output. The successive steps may be overlapped to someextent, but it is better that the heat-producing agent or Al should onlybe fed and -mixed into the advancing materials after the Ta and/or Cb iscompletely converted to the sulphide and the resulting byproducts andimpurities removed or allowed to pass out of the furnace. Referring tothe atmosphere in the furnace, it should be free of oxygen, air or otheroxygen-supplying gases for the reasons already above stated.

If it be desired to separate the conversion products, the sulphides ofTa and Cb, before reduction, the following way may be practiced.

Noting from the table of proper-ties supra that the solubili-ties ofthese compounds difier it is .only; necessary to dissolveou-t one fromthe other. .Of-course, at the outset, the mentioned oxides, chlorides orfluorides of Ta and Cb may be anutuaily separated if desired, followedby separate sulphidizing and reduction of each metal.

I What is claimed is:

1. The thermal process for treating starting material containing a metalcompound selected from the group consisting of tantalum pentoxide,columbium pentoxide, tantalum pentachloride, columbium pentachloride,tantalum pentafiuoride, columbium pentafiuoride and mixtures theerof, toconvert such compound to the sulphide; said process comprising mixingwith such starting material, in powdery form, a sulphidiz- .ing agent,and an alkaline-earth hydride; and in a non-oxidizing atmospheresubjecting such mixture to an elevated reaction temperature betweenabout 609 and 750 0., thus to bring about a reaction wherein the metalcompound contained in such starting material is chemically converted tothe sulphide, separable from other reaction products.

,2. The process as in claim 1 and wherein the starting material containsthe recited compounds of both tantalum and columbium, and during suchprocess the mixture is treated to separate from each other the tantalumand columbium constituents.

3. The process as in claim 1 and wherein the sulphidizing agent is oneselected from the group consisting of sulphur, fumes of sulphur and carbon disulphide.

4. The process as in claim 1 and wherein the sulphidizing agent iscarbon disulphide.

v5. The process as in claim 1 and wherein the alkaline-earth hydride isone selected from the group consisting of calcium hydride and bariumhydride, used in powdery form.

6. The process as in claim 1 and wherein the alkaline-earth hydride iscalcium hydride Cal-I2.

"7. The process as in claim 1 and wherein the metal compound containedin the starting material is one selected from the group consisting oftantalum pentoxi-de and columbium pentoxide.

8. The process as in claim 1 and wherein the metal compound contained inthe starting material is one selected from the group consisting oftantalum pentachloride and columbium pentachloride.

9. The thermal process for treatin starting material containing a metalcompound selected from the group consisting of tantalum pentoxide andcolumbium pentoxide and mixtures thereof, to convert such compound tothe sulphide; said process comprising mixing with such starting materialas a sulphidizing agent carbon disulphide, and as an alkaline-earthhydride, calcium hydride, in an oxygen-free atmosphere and under anelevated temperature between about 600 and 750 0.; thus to bring about areaction wherein the carbon and hydrogen constituents pass oiT in theform of gas, leaving behind the aforesaid sulphide and anhydrous calciumoxide; and thereupon separating away such calcium oxide by dissolving itin hydrochloric acid.

10. The thermal process for treating'starting material containing ametal compound selected from the group consisting of tantalumpentachloride and columbium pentachloride and rnixtures thereof, toconvert such compound to the sulphide; said process comprising mixingwith such starting material as a sulphidizing agent carbon disulphide,and as an alkaline-earth hydride, calcium hydride, in an oxygen-freeatmos phere and under an elevated temperature between about 600 and 7500.; thus to bring about a reaction wherein the carbon and hydrogenconstituents pass off in the form of gas, leaving behind the aforesaidsulphide and calcium chloride; and thereupon separating away suchcalcium chloride by leaching it with water.

DANIEL GARDNER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Mellor, Comprehensive Treatise onInorganic and Theoretical Chemistry, vol. 9, 1929, Longmans, Green 8:Co., New York, pages 924 and 925.

1. THE THERMAL PROCESS FOR TREATING STARTING MATERIAL CONTAINING A METALCOMPOUND SELECTED FROM THE GROUP CONSISTING OF TANTALUM PENTOXIDE.COLUMBIUM PENTOXIDE, TANTALUM PENTACHLORIDE, COLUMBIUM PENTACHLORIDE,TANTALUM PENTAFLUORIDE, COLUMBIUM PENTAFLUORIDE AND MIXTURES THEREOF, TOCONVERT SUCH COMPOUND TO THE SULPHIDE; SAID PROCESS COMPRISING MIXINGWITH SUCH STARTING MATERIAL, IN POWDERY FORM, A SULPHIDIZING AGENT, ANDAN ALKALINE-EARTH HYDRIDE; AND IN A NON-OXIDIZING ATMOSPHERE SUBJECTINGSUCH MIXTURE TO AN ELEVATED REACTION TEMPERATURE BETWEEN ABOUT 600* AND750* C., THUS TO BRING ABOUT A REACTION WHEREIN THE METAL COMPOUNDCONTAINED IN SUCH STARTING MATERIAL IS CHEMICALLY CONVERTED TO THESULPHIDE, SEPARABLE FROM OTHER REACTION PRODUCTS.